Ablation device with ionically conductive balloon

ABSTRACT

Devices, systems, and methods for performing ablation therapy on body tissue are disclosed. An example ablation device for treating body tissue includes an ionically conductive balloon and a radio-frequency electrode that delivers RF energy into a distal section of the balloon. The balloon can have a composite structure with a non-conductive section and a conductive section. A method for fabricating a semi-permeable ablation balloon using ionizing radiation and an etching process is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.61/534,587, filed Sep. 14, 2011, which is herein incorporated byreference in its entirety.

This application is related to U.S. Provisional Application No.61/534,590, entitled “Ablation Device With Multiple Ablation Modes,”filed on Sep. 14, 2011. The content of this related application isincorporated herein by reference in its entirety for all purposes.

TECHNICAL FIELD

The present disclosure relates generally to an ablation device. Morespecifically, the present disclosure pertains to an ablation deviceincluding an ionically conductive balloon for performing radio-frequencyablation therapy on body tissue.

BACKGROUND

The treatment of cardiac arrhythmias is sometimes performed inconjunction with an ablation catheter inserted into a chamber of theheart or in one of the vessels leading into or from the heart. In thetreatment of atrial fibrillation, for example, a radio frequency (RF)ablation catheter equipped with a number of electrodes can be broughtinto contact with cardiac tissue for creating one or more ablationpoints along the tissue. During ablation, an RF generator supplieselectrical energy to the electrodes, generating an electric field in thetissue. The resulting heat from this electric field forms a controlledlesion that blocks the electrical impulses from being conducted throughthe tissue and serves to promote the normal conduction of electricalimpulses through the proper electrical pathway within the heart.

In certain catheter ablation procedures, it may be difficult toelectrically isolate the tissue to be treated. In the treatment ofparoxysmal atrial fibrillation, for example, it is often tedious andtime consuming to isolate the pulmonary veins using an ablation catheterhaving an ablation electrode that directly contacts the tissue.Moreover, the ablations created by some ablation electrodes can causedehydration in the tissue, which can result in scarring andcalcification as the lesion heals. Due to the discrete nature of theablation points, there is also the potential for leaving small gaps ofelectrically conductive tissue in the ablation line that may continue toinitiate points of arrhythmias.

SUMMARY

The present disclosure relates generally to an ablation device includingan ionically conductive balloon for performing radio-frequency ablationtherapy on body tissue.

In Example 1, an ablation device for treating body tissue, comprises: anelongate shaft having a proximal section, a distal section, and at leastone fluid lumen configured to receive an electrically conductive fluid;an inflatable balloon coupled to the distal section of the shaft andincluding an interior section in fluid communication with the at leastone fluid lumen for actuating the balloon between a collapsed state andan expanded state, wherein the balloon comprises a composite structurehaving a proximal balloon section including a first polymeric materialand a distal balloon section including a second polymeric materialdifferent from the first material; and at least one electrode locatedwithin the interior space of the balloon.

In Example 2, the ablation device according to Example 1, wherein thefirst polymeric material is a hydrophobic polymer.

In Example 3, the ablation device according to any of Examples 1-2,wherein the second polymeric material is a hydrophilic polymer.

In Example 4, the ablation device according to any of Examples 1-3,further comprising at least one additional fluid lumen for recirculatingfluid through the device.

In Example 5, the ablation device according to any of Examples 1-4,wherein, in the expanded state, the balloon is conically shaped.

In Example 6, the ablation device according to any of Examples 1-5,wherein the distal section of the balloon is invaginated.

In Example 7, the ablation device according to any of Examples 1-6,wherein the distal section of the balloon is semi-permeable.

In Example 8, the ablation device according to any of Examples 1-7,wherein a thickness of the balloon tapers along a length of the balloonfrom the proximal balloon section to the distal balloon section.

In Example 9, the ablation device according to any of Examples 1-8,wherein the balloon comprises a multi-layered structure.

In Example 10, the ablation device according to any of Examples 1-9,further comprising a temperature sensing element coupled to the distalsection of the balloon.

In Example 11, the ablation device according to any of Examples 1-10,further comprising at least one electrocardiogram sensor coupled to thedistal section of the balloon.

In Example 12, the ablation device according to any of Examples 1-11,further comprising a spring-actuated plunger assembly configured to biasthe balloon in the collapsed state.

In Example 13, the ablation device according to Example 12, wherein theplunger assembly comprises a plunger mechanism and a spring configuredto bias the plunger mechanism against the balloon.

In Example 14, the ablation device according to Example 13, wherein theplunger mechanism includes a plunger shaft and an atraumatic tip.

In Example 15, the ablation device according to Example 14, wherein theplunger shaft is slidably disposed within the catheter shaft and theelectrode.

In Example 16, an ablation device for treating body tissue comprises: anelongate shaft having a proximal section, a distal section, and at leastone fluid lumen configured to receive an electrically conductive fluid;an inflatable balloon coupled to the distal section of the shaft andincluding an interior section in fluid communication with the at leastone fluid lumen for actuating the balloon between a collapsed state andan expanded state; at least one electrode located within the interiorspace of the balloon; and a spring mechanism configured to bias theballoon in the collapsed state.

In Example 17, a method of forming a balloon of an ablation catheter,the balloon having a proximal section and a distal section, the methodcomprising: masking the proximal section of the balloon; irradiating thedistal section of the balloon with an ionizing radiation source; etchingthe balloon to form a plurality of micropores through the distal sectionof the balloon; and securing the balloon to a catheter.

In Example 18, the method according to Example 17, wherein the ionizingradiation source comprises an argon ion source.

In Example 19, the method according to any of Examples 17-18, whereinthe proximal section of the balloon comprises a hydrophobic polymer andthe distal section of the balloon comprises a hydrophilic polymer.

In Example 20, the method according to any of Examples 17-19, wherein apore size of the micropores is between about 0.1 microns to 5 microns indiameter.

In Example 21, a system for ablating body tissue comprises: an RFgenerator including a switching mechanism operable between a firstposition and a second position; a fluid source including a supply ofelectrically conductive fluid; and an ablation device, the ablationdevice including an elongate shaft having a proximal section, a distalsection, and at least one fluid lumen; an inflatable balloon coupled tothe distal section of the shaft and including an interior section influid communication with the fluid source for actuating the balloonbetween a collapsed state and an expanded state; a first electrodedisposed within the interior space of the balloon and electricallycoupled to the RF generator, the first electrode configured forsupplying a first RF electrical field through the balloon and into thebody tissue when operating in the first position; a second electrodecoupled to a distal end portion of the elongate shaft and electricallycoupled to the RF generator, the second electrode configured forsupplying a second RF electric field directly into the tissue whenoperating in the second position.

In Example 22, the system according to Example 21, wherein the ballooncomprises a composite structure having a proximal balloon sectionincluding a hydrophobic polymeric material and a distal balloon sectionincluding a hydrophilic polymeric material.

In Example 23, the system according to any of Examples 21-22, wherein,in the expanded state, the balloon is conically shaped.

In Example 24, the system according to any of Examples 21-23, whereinthe distal section of the balloon is invaginated.

In Example 25, the system according to any of Examples 21-24, whereinthe distal section of the balloon is semi-permeable.

In Example 26, the system according to any of Examples 21-25, wherein athickness of the balloon tapers along a length of the balloon from aproximal balloon section to a distal balloon section.

In Example 27, the system according to any of Examples 21-26, whereinthe balloon comprises a multi-layered structure.

In Example 28, the system according to any of Examples 21-27, furthercomprising a spring-actuated plunger assembly configured to bias theballoon in the collapsed state.

In Example 29, a method for performing ablation therapy on the body of apatient comprises: advancing an ablation device to a target body tissueregion, the ablation device including an inflatable balloon coupled toan elongate shaft, a first electrode disposed within an interior spaceof the balloon, and a second electrode located outside of the balloon;injecting an electrically conductive fluid into the interior section ofthe balloon and inflating the balloon from a collapsed state to anexpanded state within the body; selectively energizing the firstelectrode and generating a first RF electrical field within the ballooninterior; forming at least one ablation lesion within the body tissueusing the first RF electrical field; selectively energizing the secondelectrode and generating a second RF electrical field; and forming atleast one ablation lesion within the body tissue using the second RFelectrical field.

In Example 30, the method according to Example 29, further comprising anRF generator including a switching mechanism, and wherein selectivelyenergizing the first or second electrodes includes operating theswitching mechanism between a first and second switch position.

In Example 31, the method according to any of Examples 29-30, whereinforming at least one ablation lesion within the body tissue using thefirst RF electrical field includes forming a lesion in the body tissueat a location distal to the elongate shaft.

In Example 32, the method according to any of Examples 29-31, whereinthe at least one ablation lesion formed within the body tissue using thefirst RF electric field is larger than the at least one ablation lesionformed in the body tissue using the second RF electric field.

In Example 33, an ablation device for treating body tissue comprises: anelongate shaft having a proximal section, a distal section, and at leastone fluid lumen configured to receive an electrically conductive fluid;an inflatable balloon coupled to the distal section of the shaft andincluding an interior section in fluid communication with the at leastone fluid lumen for actuating the balloon between a collapsed state andan expanded state; and at least one electrode located within theinterior space of the balloon, the at least one electrode configured fortransmitting an RF electric field through the balloon and into bodytissue in contact with the balloon; wherein the balloon is configured totransmit the RF electric field in a direction distally towards a leadingend of the ablation device.

In Example 34, the ablation device according to Example 33, wherein theballoon comprises a composite structure having a proximal balloonsection including a hydrophobic polymeric material and a distal balloonsection including a hydrophilic polymeric material.

In Example 35, the ablation device according to any of Examples 33-34,wherein, in the expanded state, the balloon is conically shaped.

In Example 36, the ablation device according to any of Examples 33-35,wherein the distal section of the balloon is invaginated.

In Example 37, the ablation device according to any of Examples 33-36,wherein the distal section of the balloon is semi-permeable.

In Example 38, the ablation device according to any of Examples 33-37,wherein a thickness of the balloon tapers along a length of the balloonfrom a proximal balloon section to a distal balloon section.

In Example 39, the ablation device according to any of Examples 33-38,wherein the balloon comprises a multi-layered structure.

In Example 40, the ablation device according to any of Examples 33-39,further comprising a spring-actuated plunger assembly configured to biasthe balloon in the collapsed state.

While multiple embodiments are disclosed, still other embodiments of thepresent invention will become apparent to those skilled in the art fromthe following detailed description, which shows and describesillustrative embodiments of the invention. Accordingly, the drawings anddetailed description are to be regarded as illustrative in nature andnot restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an ablation device in accordance with anillustrative embodiment;

FIG. 2 is a partial cross-sectional view showing the distal section ofthe ablation device of FIG. 1 in a collapsed state;

FIG. 3 is another partial cross-sectional view showing the distalsection of the ablation device of FIG. 1 in an expanded state;

FIG. 4 is a flow diagram showing an example method for fabricating aporous balloon of an ablation device;

FIG. 5 is a perspective view showing an example composite balloon inaccordance with an illustrative embodiment;

FIG. 6 is a partial cross-sectional view showing the distal section ofan ablation device in accordance with another illustrative embodiment;

FIG. 7 is a partial cross-sectional view showing the distal section ofan ablation device in accordance with another illustrative embodiment;

FIG. 8 is a partial cross-sectional view showing the distal section ofan ablation device in accordance with another illustrative embodiment;

FIG. 9 is a schematic view of an ablation device in accordance withanother illustrative embodiment; and

FIG. 10 is a flow diagram of an illustrative method of performing acardiac ablation procedure using the ablation device of FIG. 9.

While the invention is amenable to various modifications and alternativeforms, specific embodiments have been shown by way of example in thedrawings and are described in detail below. The intention, however, isnot to limit the invention to the particular embodiments described. Onthe contrary, the invention is intended to cover all modifications,equivalents, and alternatives falling within the scope of the inventionas defined by the appended claims.

DETAILED DESCRIPTION

FIG. 1 is a schematic view of an ablation device 10 in accordance withan illustrative embodiment. As shown in FIG. 1, the ablation device 10includes an elongate shaft 12 having a proximal section 14, a distalsection 16, and at least one lumen 18 extending through the shaft 12between the proximal and distal sections 14, 16. An inflatable ablationballoon 20 coupled to the distal section 16 of the shaft 12 can beinflated at a target location within the body (e.g., within a cardiacvessel) and brought into contact with the body tissue to be treated. Insome embodiments, and as further described below, an RF electrodeassembly 22 located within an interior portion of the balloon 20generates an RF electric field that can be used for creating controlledlesions within the tissue. In the treatment of paroxysmal atrialfibrillation, for example, the balloon 20 and the RF electrode assembly22 can be used for performing electrical isolation within a pulmonaryvein to prevent the aberrant conduction of electrical signals within theleft side of the heart. The ablation device 10 can also be used fortreating other types of cardiac arrhythmias and/or cardiovasculardiseases within the body. The ablation device 10 can also be used fortreating other conditions commonly performed by ablation devices.

A handle 24 coupled to the proximal section 14 of the shaft 12 can beused by the clinician for manipulating and steering the distal section16 to a target site within the body for performing an ablation. In someembodiments, the handle 24 includes a fluid port 26 and valve 28 influid communication with a source of electrically conductive fluid 30.In some embodiments, for example, the fluid 30 can comprise saline or asolution of saline and a fluoroscopic contrast medium that is bothconductive and biocompatible. During an ablation procedure, pressurizedfluid 30 can be delivered via the fluid lumen 18 to the interior of theballoon 20, causing the balloon 20 to inflate while also creating anelectrical pathway between the electrode 22 and the portion of theballoon 20 in contact with the body tissue to be treated. In someembodiments, multiple fluid ports can be provided to recirculate thefluid 30 through the ablation device 10 as part of a closed-loop systemfor controlling the temperature within the balloon 20.

In some embodiments, the ablation device 10 further includes a steeringmechanism 32 that can be used to mechanically steer the distal section16 of the shaft 12 within the body. In certain embodiments, for example,the steering mechanism 32 comprises a slider or lever mechanism on thehandle 24 that can be actuated by the clinician to engage a number ofsteering wires located within the shaft 12. During delivery of thedevice 10 to a target region within the body, the steering mechanism 32can be engaged to deflect the distal section 16 of the shaft 12,allowing the clinician to better navigate the device 10 through thevasculature.

An RF generator 34 is configured to supply radio-frequency energy to theelectrode assembly 22. In some embodiments, the device 10 is configuredto operate in a bipolar mode, in which ablation energy supplied by theRF generator 34 flows from one electrode of the electrode assembly 22 toanother electrode of the electrode assembly 22 or provided at adifferent location along the device 10 (e.g., along the distal section16 of the shaft 12). In other embodiments, the device 10 is configuredto operate in a unipolar mode, in which an indifferent electrode (e.g.,an electrode patch) is attached to the patient's back or other exteriorskin area and ablation energy from the RF generator 34 flows from oneelectrode of the assembly 22 to the indifferent electrode.

FIG. 2 is a partial cross-sectional view showing the distal section 16of the ablation device 10 of FIG. 1 in greater detail. As can be furtherseen in FIG. 2, and in some embodiments, the electrode assembly 22comprises at least one RF electrode 36 located within an interior space38 of the balloon 20. The RF electrode 36 is fixedly secured to a distalend 40 of the shaft 12 (e.g., using a suitable adhesive at both ends ofthe electrode 36), and is electrically coupled to the RF generator 34.In the embodiment of FIG. 2, the RF electrode 36 comprises a metaltubular member made from a suitably conductive metal such as platinum,and is electrically coupled to the RF generator 34 via a number ofconductor wires (not shown) located within the shaft 12. Theconfiguration of the RF electrode 36 can vary from that shown, however.For example, the RF electrode 36 can comprise a coil, ring, flat ribbon,or other suitable shape. In some embodiments, the electrode assembly 22can include multiple electrodes 36 as part of either a bipolar RFablation system, or as part of a unipolar system with multipleelectrodes.

The device 10 includes at least one fluid lumen for transmittingpressurized fluid 30 to the interior space 38 of the balloon 20. In theembodiment of FIG. 2, the device 10 includes a central fluid lumen 18that extends longitudinally through the shaft 12 and through a portionof the RF electrode 36. In some embodiments, the fluid lumen 18terminates distally at a number of inflation ports 42 disposedcircumferentially about the RF electrode 36. In some embodiments, thesame fluid lumen 18 can be used for both inflating and deflating theballoon 20. In other embodiments, separate fluid lumens are used forinflating and deflating the balloon 20. Such a configuration can providecontinuous infusion and evacuation of fluid within the balloon 20 tomaintain both a controlled operating pressure and temperature within theballoon 20. In one embodiment, multiple fluid lumens within the shaft 12may permit the electrically conductive fluid 30 to be recirculatedthrough the device 10 during the ablation procedure. The fluid 30 canalso include a contrast medium to facilitate visualization of theballoon 20 under fluoroscopy.

In the embodiment of FIG. 2, the balloon 20 is coupled to the distalsection 16 of the shaft 12 at or near the distal shaft end 40, and isinflatable from an initial, collapsed position having a low-profile thatfacilitates traversal of the device 10 through the body, to a second,expanded position that contacts and engages the body tissue to beablated. In certain embodiments, the balloon 20 has a compositestructure formed from different polymeric materials, which helps todirect and focus the RF energy from the RF electrode 36 into the bodytissue located at or near a distal end 44 of the balloon 20. In oneembodiment, for example, the composite balloon 20 includes a proximal,non-conductive section 46 a made from a hydrophobic polymer and adistal, conductive section 46 b made from a hydrophilic polymer. Thepolymer of the non-conductive section 46 a can be non-ionicallyconductive and the polymer of the distal section 46 b can be ionicallyconductive. In some embodiments, for example, the composite balloonstructure can comprise a proximal section 46 a made from a hydrophobicpolyurethane material and a distal section 46 b made from a hydrophilicpolyurethane material such as TECOPHILIC 60D®, available from ThermedicsPolymer Products of Woburn, Mass. TECOPHILIC® is a polyether-basedaliphatic polyurethane and exhibits sufficient elasticity so as to becapable of stretching substantially beyond its equilibrium dimensionswhen the balloon 20 is inflated. Other polymeric materials can also beused to impart differing hydrophilic characteristics to the proximal anddistal sections 46 a, 46 b. As used herein, the term “hydrophilic”indicates that the polymer, when in contact with an aqueous solution,can absorb a quantity of water while still maintaining its structuralintegrity.

When inflated with the electrically conductive fluid 30, the distalsection 46 b of the composite balloon 20 is rendered conductive byhydration due to the ionic content of the fluid 30 when the RF energy issupplied to the RF electrode 36. As a result, electrical current istransmitted through the fluid 30 and into the tissue in contact with thedistal section 46 b of the balloon 20. In some cases, current passesthrough all areas of the balloon material that are hydrophilic but doesnot pass through areas of the balloon that are hydrophobic ornon-conductive.

The composite balloon structure can be formed using a number ofdifferent techniques. For example, the different sections 46 a, 46 b ofthe balloon 20 can be formed by separately dip-coating each section ofthe balloon 20 on a mandrel that has a defined size and shape. Theballoon 20 can also be formed using other techniques, such as byspin-coating in a hollow mold or by injection or blow-molding. Anotherexample method for constructing a composite balloon structure having apermeable or semi-permeable distal section is discussed further hereinwith respect to FIG. 4.

In some embodiments, the device 10 further includes one or moretemperature sensing elements that can be used to sense the temperatureof fluid 30 within the balloon 20. In certain embodiments, and as shownin FIG. 2, a temperature sensing element 48 such as a thermocouple orthermistor is coupled to the inner surface 50 of the balloon 20 at thedistal section 46 b. In other embodiments, the temperature sensingelement 48 is coupled to an outer surface 52 of the balloon 20 at thedistal section 46 b, or is coupled to another portion of the balloon 20or to the shaft 12. In another embodiment, the temperature sensingelement 48 is encased within the interior of the balloon material. Insome embodiments, multiple temperature sensing elements can be coupledto the inner and/or outer surfaces 50, 52 of the balloon and/or to theshaft 12 for sensing temperature at multiple locations. In variousembodiments, a temperature sensor is located on the outer surface of theballoon and/or within the wall of the balloon. Such a configuration canmeasure the temperature of the tissue undergoing ablation. In these orother embodiments referenced herein, the intensity of ablation therapy(e.g., power) can be automatically modulated based on the measuredtemperature to limit the temperature of the tissue undergoing ablation.Such a configuration can provide protection from steam pops, where asmall gaseous rupture in tissue can otherwise be created by water in thetissue turning into steam when the temperature reaches 1000 C orgreater.

In some embodiments, the temperature sensing element 48 senses thetemperature of the fluid 30 contained within the interior section 38 ofthe balloon 20, and is connected to temperature sensing circuitry (e.g.,based on a thermometer) located outside of the body. During ablation,the RF generator 34 can be controlled so as to adjust the temperature ofthe fluid 30 contained in the balloon 20 to a desired temperature. Inthose embodiments in which multiple fluid ports are utilized forrecirculating fluid through the device 10, the flow of fluid can also becontrolled based on feedback from the temperature sensing element 48 tomaintain the fluid within the balloon 20 at a particular temperature orwithin a range of temperatures.

One or more electrocardiogram sensors coupled to the balloon 20 can alsobe used in some embodiments for sensing electrical activity in or nearthe heart. In the embodiment of FIG. 2, for example, anelectrocardiogram sensor 54 is coupled to the inner surface 50 of theballoon 20 at the distal section 46 b, allowing the clinician to monitorfor the presence of any electrical activity at the target ablation site.In other embodiments, the electrocardiogram sensor 54 is coupled to theouter surface 52 of the balloon 20 at the distal section 46 b, or iscoupled to another portion of the balloon 20 or shaft 12. In anotherembodiment, the electrocardiogram sensor 54 is encased within theinterior of the balloon material. In some embodiments, multipleelectrocardiogram sensors can be coupled to and/or encased within theballoon 20 and/or to the shaft 12 for sensing electrical activity atmultiple locations.

A spring actuated plunger assembly 56 can be used to maintain theballoon 20 in a collapsed, low-profile position to facilitate deliveryof the device 10 through the body prior to inflating the balloon 20 atthe desired target tissue location. In the embodiment of FIG. 2, theassembly 56 includes a plunger mechanism 58 and a spring 60. The spring60 is located within the interior of the shaft 12 proximal to the RFelectrode 36, and is configured to mechanically bias the plungermechanism 58 in a distal direction towards the distal end 44 of theballoon 20, thus maintaining the balloon 20 in an extended positionuntil inflated.

In some embodiments, the plunger mechanism 58 comprises a plunger shaft62 slidably disposed within the interior section 38 of the balloon 20and through a portion of the RF electrode 36. The distal end of theplunger shaft 62 includes an atraumatic tip 64 which, when the plungermechanism 58 is fully engaged distally, is configured to contact andengage the distal end 44 of the balloon 20 causing the balloon 20 tocollapse and assume a low-profile position, as shown. The shape of thetip 64 is curved to conform to the shape of the balloon 20 at the distalend 44. The proximal end of the plunger shaft 62 is coupled to a plungerseal 66, which provides a surface against which the spring 60 engagesthe plunger shaft 62. A shoulder 68 located within the interior of theshaft 12 proximal to the spring 60 provides a proximal stop to preventproximal movement of the spring 60 when the spring 60 is compressed.

FIG. 3 is another partial cross-sectional view of the ablation device 10of FIG. 1, showing the balloon 20 in a second, fully expanded position.As can be further seen in FIG. 3, when pressurized fluid 30 is injectedinto the interior section 38 of the balloon 20, the fluid pressureexerted against the surface of the plunger seal 66 is configured toovercome the spring bias provided by the spring 60, causing the spring60 to move to a second, compressed position within the shaft interior.Once the balloon 20 is inflated, the pressure within the interiorsection 38 of the balloon 20 pushes the plunger assembly 56 in aproximal direction. As a result, the plunger shaft 62 is drawnproximally into the shaft interior, causing the atraumatic tip 64 todisengage from the distal end 44 of the balloon 20.

When the tip 64 disengages from the distal end 44 of the balloon 20, andas shown in FIG. 3, the balloon 20 is configured to expand to itssecond, expanded position. In some embodiments, the shape of theinflated balloon 20 may vary along its length such that the proximalsection 46 a of the balloon 20 has a profile and shape that is differentfrom that of the distal section 46 b. In the embodiment of FIG. 3, forexample, the inflated balloon 20 has a substantially conical shape suchthat the distal, conductive section 46 b of the balloon 20 exposes arelatively large area towards the distal end 44 of the balloon 20. Theconical shape of the distal section 46 b facilitates contact of theballoon 20 with body tissue located primarily distally of the device 10.The proximal section 46 a of the balloon 20, in turn, has a relativelylow profile, and thus does not contact the body tissue. In contrast tothe distal section 46 b, the hydrophobic material of the proximalsection 46 a also does not conduct with the fluid 30 within the balloon20.

Although the illustrative balloon 20 in FIG. 3 has a conical shape whenexpanded, in other embodiments the balloon 20 can have a different shapeand/or profile when inflated. Examples of other balloon shapes caninclude elliptical, spherical, or dumbbell. In some embodiments, theballoon shape can be similar to one of the self-anchoring balloon shapesdescribed in U.S. Pat. No. 7,736,362, the contents of which areincorporated herein by reference in their entirety for all purposes.Other balloon configurations are also possible.

In some embodiments, the distal section 46 b of the balloon 20 issemi-permeable, allowing at least some of the pressurized fluid 30within the interior section 38 of the balloon 20 to seep into the bodyat or near the target ablation site. In some embodiments, the distalsection 46 b of the balloon 20 is permeable, allowing the pressurizedfluid 30 within the interior section 38 of the balloon 20 to seep intothe body at or near the target ablation site. During ablation, thepresence of the electrically conductive fluid at this interface regionaids in creating an electrical conduit for the electrical fieldgenerated by the RF electrode 36, and further serves to cool theablation site. As the RF energy is applied to the RF electrode 36 insidethe balloon 20, the RF energy is transmitted to the tissue in contactwith the balloon 20 through the electrically conductive fluid seepingthrough the balloon 20. The permeability or semi-permeability of thedistal section 46 b also permits the delivery of an agent or drugcontained within the fluid 30. In this manner, the balloon 20 may alsoact as a drug delivery device by introducing one or more drugs into theconductive fluid 30 and permitting the drugs to pass through the balloon20 and into the tissue.

FIG. 4 is a flow diagram showing an example method 70 for fabricating aporous balloon. The method 70 may begin generally at block 72, byfabricating a composite balloon having a proximal, non-conductivesection and a distal, conductive section. It is noted that in someembodiments the distal section is non-conductive. In certainembodiments, for example, a composite balloon 20 such as that shown inFIGS. 2-3 can be fabricated using a suitable process such asdip-coating, spin-coating, injection molding, or blow-molding. Otherfabricating techniques for fabricating a composite balloon can also beutilized.

The balloon material or materials can be selected so as to facilitatefurther processing steps to create micropores through the balloonmaterial. In some embodiments, for example, the workpiece used to createthe composite balloon can be formed from a thermoplastic polymer resinsuch as polyethylene terephthalate (PET). The thermal and/or chemicalcharacteristics of PET permit subsequent processing steps to beperformed on the balloon while maintaining the desired tensile strengthand elasticity characteristics of the balloon.

Once the composite balloon has been fabricated, the proximal,non-conductive section of the balloon is masked (block 74), and thedistal (e.g., conductive) section of the balloon is irradiated with ionsfrom an ionizing radiation source (block 76).

In one embodiment, the composite balloon is irradiated with Argon atomsfrom an Argon plasma source. Other suitable ionic radiation sources canalso be used to irradiate the distal section of the balloon with ions.

Once irradiated, the balloon is then subjected to a sodium hydroxide(NaOH) etching process for a period of time to produce uniformmicropores in the distal section of the balloon (block 78). In certainembodiments, for example, the balloon can be inserted into an etchingbath and treated for a period of approximately 10 to 15 minutes untilpores of a desired size are formed through the balloon material. Thepore size can be controlled by the duration of the ionizing radiationand etching steps, the strength of the ionizing radiation, and thestrength of the etching solution. Other factors such as the ballooncomposition, balloon thickness, as well as other characteristics canalso affect the pore size. An example pore size that can be generatedusing this process can be between about 0.1 microns to about 5 micronsin diameter, although other pore sizes greater or smaller are alsocontemplated. For example, in some cases pores can be up to 20 micronsin diameter.

Once the micropores are created in the distal section of the balloon,additional processing steps can then be performed to secure the balloononto the shaft (block 80). In one embodiment, the balloon can be mountedto the distal end of a shaft, similar to that shown in the illustrativeembodiment shown in FIGS. 2-3. The balloon can be secured to the shaftin a variety of ways, including adhesive bonding, thermal bonding,mechanical bonding, screws, winding, or a combination of these.

FIG. 5 is a perspective view showing an example composite balloon 20that has been treated using the method 70 of FIG. 4. As can be seen inFIG. 5, the distal section 46 b of the balloon 20 includes a pluralityof micropores 82 which, due to the size and shape of the distal section46 b in its inflated state, face substantially in a distal directionaway from the distal end 44 of the balloon 20 in the direction indicatedgenerally by arrow 84. When a steady flow of electrically conductivefluid is provided to the interior section 38 of the balloon 20, at leasta portion of the fluid seeps through the micropores 82 and into contactwith body tissue located distally of the balloon 20. The proximalsection 46 a of the balloon 20 is substantially non-porous, and thusprohibits the flow of pressurized fluid through the proximal section 46a.

FIG. 6 is a partial cross-sectional view showing the distal section ofan ablation device 86 in accordance with another illustrativeembodiment. The ablation device 86 includes an elongate shaft 88 coupledto an inflatable ablation balloon 90. The proximal section of the shaft88 (not shown) is coupled to an electrically conductive fluid source andan RF generator. In the embodiment of FIG. 6, the distal section 92 ofthe shaft 88 extends through the interior 94 of the balloon 90, andincludes a number of fluid ports 96, 98 for circulating fluid throughthe balloon interior 94. A first fluid port 96 in fluid communicationwith a first lumen within the shaft 88 is configured to deliverelectrically conductive fluid from an external fluid source into theballoon interior 94. A second fluid port 98 in fluid communication witha return fluid lumen of the shaft 88, in turn, functions as a returnport for recirculating heated fluid within the balloon interior 94 to alocation outside of the patient's body for cooling.

An electrode assembly 100 disposed within the interior 94 of the balloon90 is electrically coupled to an RF generator, and is configured togenerate an RF electric field for creating controlled lesions withintissue located adjacent to the balloon 90. In some embodiments, and asshown in FIG. 6, the electrode assembly 100 comprises a metal coil RFelectrode 102 having a helical shape that extends about a portion of theshaft 88 located within the balloon interior 94. In other embodiments,the RF electrode 102 can comprise a tubular member, ring, flat ribbon,or other suitable shape. In some embodiments, the electrode assembly 100can include multiple electrodes 102 as part of either a bipolar RFablation system, or as part of a unipolar system with multipleelectrodes.

In the embodiment of FIG. 6, a proximal section 112 a of the balloon 90is coupled to the distal section 92 of the elongate shaft 88. A distalsection 112 b of the balloon 90, in turn, is coupled to the distal end108 of the elongate shaft 88. In some embodiments, and as shown in FIG.6, the distal section 112 b of the balloon 90 has an invaginatedconfiguration created by folding or turning a portion of the balloon 90back upon itself and attaching the distal end 106 of the balloon 90 toan interior surface of the shaft distal end 108. The balloon 90 isinflatable from an initial, collapsed position having a low-profile thatfacilitates traversal of the device 86 through the body, to a second,expanded position that contacts and engages the body tissue to beablated. In some embodiments, the balloon 90 has a composite structureformed from different polymeric materials, which helps to direct andfocus the RF energy from the RF electrode 100 into body tissue locatedat or near a distal section 112 b of the balloon 90. In one embodiment,for example, the composite balloon 90 includes a proximal,non-conductive section 112 a made from a hydrophobic polymer and adistal, conductive section 112 b made from a hydrophilic polymer. Insome embodiments, for example, the composite balloon structure cancomprise a proximal section 112 a made from a hydrophobic polyurethanematerial and a distal section 112 b made from a hydrophilic polyurethanematerial such as TECOPHILIC 60D®. Other polymeric materials can also beused to impart differing hydrophilic characteristics to the proximal anddistal sections 112 a, 112 b, as desired.

When inflated with an electrically conductive fluid, the distal section112 b of the balloon 90 is rendered conductive by hydration due to theionic content of the fluid when RF energy is supplied to the RFelectrode 102. An electrical current is thus transmitted through thefluid and into the tissue in contact with the distal section 112 b ofthe balloon 90. When inflated, the invaginated configuration of theballoon 90 also serves to direct the RF electrical field towards thedistal section 112 b of the balloon 90.

The ablation device 86 can further include one or more featuresdescribed with respect to other embodiments, including one or moretemperature sensors for sensing the temperature of fluid within or onthe surface of the balloon 90, and one or more electrocardiogram sensorsfor sensing electrical activity in or near the heart. The device 86 canalso include other features such as a spring-actuated plunger assembly.In certain embodiments, the balloon 90 can also be made permeable orsemi-permeable, allowing at least some of the pressurized fluid withinthe interior section 94 of the balloon 90 to seep into the body at ornear the target ablation site.

FIG. 7 is a partial cross-sectional view showing the distal section ofan ablation device 114 in accordance with another illustrativeembodiment. The ablation device 114 includes an elongate shaft 116coupled to an inflatable ablation balloon 118. The proximal section ofthe shaft 116 is coupled to an electrically conductive fluid source andan RF generator. In the embodiment of FIG. 7, the distal section 120 ofthe shaft 116 extends through the interior 122 of the balloon 118, andincludes a number of fluid ports 124, 126 for circulating fluid throughthe balloon interior 122. A first fluid port 124 in fluid communicationwith a first lumen within the shaft 116 is configured to deliverelectrically conductive fluid from an external fluid source into theballoon interior 122. A second fluid port 126 in fluid communicationwith a return fluid lumen within the shaft 116, in turn, functions as areturn port for recirculating heated fluid within the balloon interior122 to a location outside of the patient's body for cooling.

An electrode assembly 128 disposed within the interior 122 of theballoon 118 is electrically coupled to an RF generator, and isconfigured to generate an RF electric field for creating controlledlesions within tissue located adjacent to the balloon 118. In someembodiments, and as shown in FIG. 7, the electrode assembly 128comprises a metal coil RF electrode 130 having a helical shape thatextends about a portion of the shaft 116 located within the ballooninterior 122. In other embodiments, the RF electrode 130 can comprise atubular member, ring, flat ribbon, or other suitable shape. In someembodiments, the electrode assembly 128 can include multiple electrodes130 as part of either a bipolar RF ablation system, or as part of aunipolar system with multiple electrodes.

In the embodiment of FIG. 7, a proximal end portion 132 of the balloon118 is coupled to the distal section 120 of the elongate shaft 118. Theballoon 118 is inflatable from an initial, collapsed position having alow-profile that facilitates traversal of the device 114 through thebody, to a second, expanded position that contacts and engages the bodytissue to be ablated. In some embodiments, and as shown, the thicknessof the balloon 118 can taper along a length of the balloon 118 that isgenerally parallel with the shaft 116 such that the thickness of theproximal section 134 a is greater than the thickness of the distalsection 134 b. In certain embodiments, the thickness of the balloon 118tapers continuously along the length of the balloon 118 between theproximal and distal sections 134 a, 134 b. In one embodiment, forexample, the balloon 118 may continuously taper from a thickness ofbetween about 5 mils (0.005 inches) to 15 mils (0.015 inches) at or nearthe location 132 where the proximal section 134 a of the balloon 118attaches to the elongate shaft 116, to a thickness of between about 0.5mil to 5 mils at or near a distal end portion 136 of the balloon 118.

In other embodiments, the balloon 118 may transition in thickness at oneor more discrete locations along the length of the balloon 118 such thatthe thickness of the proximal section 134 a is greater than thethickness of the distal section 134 b. In one embodiment, for example,the balloon 118 thickness may transition from a relatively thickconfiguration at the proximal portion 134 a of the balloon 118 to arelatively thin configuration at the distal section 134 b of the balloon118 at a location substantially midway along the length of the balloon118. The balloon 118 may also stepwise transition in thickness atmultiple locations along the proximal and/or distal sections 134 a, 136b of the balloon 118. Other configurations are also possible.

The balloon 118 can comprise a hydrophilic polymer that facilitates thetransmission of the electromagnetic field generated by the RF electrode130 through the balloon material and into contact with the tissue. Insome embodiments, the balloon 118 comprises a composite structure inwhich multiple materials are used to transition the balloon 118 from arelatively hydrophobic composition along proximal section 134 a of theballoon 118 to a relatively hydrophilic composition along the distalsection 134 b of the balloon 118. In some embodiments, for example, thecomposite balloon structure can comprise a proximal section 134 a madefrom a hydrophobic polyurethane material and a distal section 134 b madefrom a hydrophilic polyurethane material such as TECOPHILIC 60D®, asdiscussed herein. The resulting structure is a composite balloon 118that transitions both in material composition and in thickness along thelength of the balloon 118. During an ablation, this reduction inthickness, (and in some embodiments also a change in materialcomposition) along the length of the balloon 118 causes a greater amountof the electric field generated by the RF electrode 130 to pass throughthe distal section 134 b of the balloon 118, allowing the clinician totarget body tissue that is situated distally of the balloon 118.

The ablation device 114 can further include one or more featuresdescribed with respect to other embodiments herein, including one ormore temperature sensors for sensing the temperature of fluid within oron the outer surface of the balloon 118 and/or one or moreelectrocardiogram sensors for sensing electrical activity in or near theheart. The device 114 can also include other features such as aspring-actuated plunger assembly. In certain embodiments, the balloon118 can also be made permeable or semi-permeable, allowing at least someof the pressurized fluid within the interior section 122 of the balloon118 to seep into the body at or near the target ablation site.

FIG. 8 is a partial cross-sectional view showing the distal section ofan ablation device 138 in accordance with another illustrativeembodiment. The ablation device 138 includes an elongate shaft 140coupled to an inflatable ablation balloon 142. The proximal section ofthe shaft 140 is coupled to an electrically conductive fluid source andan RF generator. In the embodiment of FIG. 8, the distal section 144 ofthe shaft 140 extends through the interior 146 of the balloon 142, andincludes a number of fluid ports 148, 150 for circulating fluid throughthe balloon interior 146. A first fluid port 148 in fluid communicationwith a first lumen within the shaft 140 is configured to deliverelectrically conductive fluid from an external fluid source into theballoon interior 146. A second fluid port 150 in fluid communicationwith a return fluid lumen within the shaft 140, in turn, functions as areturn port for recirculating heated fluid within the balloon interior146 to a location outside of the patient's body for cooling.

An electrode assembly 152 disposed within the interior 146 of theballoon 142 is electrically coupled to an RF generator, and isconfigured to generate an RF electric field for creating controlledlesions within tissue located adjacent to the balloon 142. In someembodiments, and as shown in FIG. 8, the electrode assembly 152comprises a metal coil RF electrode 154 having a helical shape thatextends about a portion of the shaft 140 located within the ballooninterior 146. In other embodiments, the RF electrode 154 can comprise atubular member, ring, flat ribbon, or other suitable shape. In someembodiments, the electrode assembly 152 can include multiple electrodes154 as part of either a bipolar RF ablation system, or as part of aunipolar system with multiple electrodes.

In the embodiment of FIG. 8, a proximal end portion 156 of the balloon142 is coupled to the distal section 144 of the elongate shaft 140. Theballoon 142 is inflatable from an initial, collapsed position having alow-profile that facilitates traversal of the device 138 through thebody, and a second, expanded position that contacts and engages the bodytissue to be ablated. In some embodiments, and as shown in FIG. 8, theballoon 142 comprises a multi-layered structure having a first layer 158and a second layer 160. The first layer 158 of the balloon 142 comprisesa hydrophilic hydratable, ionically conductive material layer thatextends across the entire surface area of the balloon 142, along both aproximal section 162 a and a distal section 162 b of the balloon 142. Incertain embodiments, for example, the first layer 158 comprises ahydrophilic polyurethane material such a TECOPHILIC 60D®. In certainembodiments, the thickness of the first layer 158 is between about 1 milto 3 mils.

In some embodiments, first layer 158 has a uniform thickness along theentire length of the balloon 142. In other embodiments, the thickness ofthe first layer 158 may transition in thickness along the length of theballoon 142. For example, in some embodiments, the first layer 158 ofthe balloon 142 may taper in thickness along the length of the balloon142 such that the portion of first layer 158 located along the proximalsection 162 a of the balloon 142 is thicker than the portion of thefirst layer 158 located along the distal section 162 b. The thickness ofthe first layer 158 can taper either continuously or at one or morediscrete locations along the length of the balloon 142. In someembodiments, the thickness of the first layer 158 may transition inthickness from about 3 mils at or near the location where the proximalend portion 156 of the balloon 142 attaches to the elongate shaft 140 toa thickness of about 1 mil at or near the distal end portion 164 of theballoon 142.

The second layer 160 of the balloon 142 comprises a hydrophobicmaterial, and extends across only a portion of the balloon 142. In theembodiment of FIG. 8, for example, the second layer 160 is located alongonly the proximal section 162 a of the balloon 142. In some embodiments,the second layer 160 comprises a hydrophobic polymer mask that isspray-coated onto the first layer 158 during the balloon manufacturingprocess. Other techniques can also be used for forming the second layer160, including sputtering, adhesion, or co-extrusion.

In the embodiment of FIG. 8, the thickness of the second layer 160tapers continuously along its length. In other embodiments, the secondlayer 160 reduces in thickness at one or more discrete locations alongits length. In some embodiments, the thickness of the second layer 160may transition from between about 5 mils at or near the location wherethe proximal end portion 156 of the balloon 142 attaches to the elongateshaft 140 to a thickness of about 1 mil at or near the location wherethe second layer 160 terminates.

During ablation, the presence of the hydrophobic second layer 160 overthe first layer 158 of the balloon 142 causes a greater amount of theelectrical field generated by the RF electrode 154 to pass through thedistal section 162 b of the balloon 142, allowing the clinician totarget body tissue that is situated distally of the balloon 142. In somecases during ablation, the presence of the hydrophobic second layer 160over the first layer 158 of the balloon 142 causes the RF current to beconcentrated and evenly distributed through only the unmaskedhydrophilic distal surface of the balloon, allowing the clinician totarget body tissue that is situated distally of the balloon 142.

The ablation device 138 can further include one or more featuresdescribed with respect to other embodiments, including one or moretemperature sensors for sensing the temperature of fluid within or onthe surface of the balloon and/or one or more electrocardiogram sensorsfor sensing electrical activity in or near the heart. The device 138 canalso include other features such as a spring-actuated plunger assembly.In certain embodiments, the balloon 142 can also be made permeable orsemi-permeable, allowing at least some of the pressurized fluid withinthe interior 146 of the balloon 142 to seep into the body at or near thetarget ablation site.

FIG. 9 is a schematic view of an ablation device 166 in accordance withanother illustrative embodiment. The ablation device 166 includes anelongate shaft 168 having a proximal section 170, a distal section 172,and at least one lumen 173 extending through the shaft 168 between theproximal and distal sections 170, 172. An inflatable balloon 174 coupledto the distal section 172 of the shaft 168 can be inflated at a targetlocation within the body and brought into contact with the body tissueto be treated. In the embodiment of FIG. 9, the distal section 172 ofthe shaft 168 extends through an interior 176 of the balloon 174, andincludes a number of fluid ports 178, 180 for circulating fluid throughthe balloon interior 176. A first fluid port 178 in fluid communicationwith a first lumen within the shaft 168 is configured to deliverelectrically conductive fluid from an external fluid source into theballoon interior 176. A second fluid port 180 in fluid communicationwith a return fluid lumen within the shaft 168, in turn, functions as areturn port for recirculating heated fluid within the balloon interior176 to a location outside of the patient's body for cooling.

An electrode assembly 182 disposed within the interior 176 of theballoon 174 is electrically coupled to an RF generator 34 that can beused to generate an RF electric field for creating controlled lesionswithin tissue. In the embodiment of FIG. 9, the electrode assembly 182includes a first electrode 184 and a second electrode 186. The firstelectrode 184 comprises a metal coil RF electrode having a helical shapethat extends about a portion of the shaft 168 located within the ballooninterior 176. In other embodiments, the first electrode 184 can comprisea tubular member, ring, flat ribbon, or other suitably shaped electrode.The second electrode 186, in turn, is coupled to the distal end portion188 of the elongate shaft 168, and is located outside of the balloon 174and directly contacts the body tissue to be ablated.

In some embodiments, the RF generator 34 includes a switch 190 forselectively activating either the first electrode 184 or the secondelectrode 186. In one embodiment, and as shown, the switch 190 includesa first electrical wire 192 electrically coupled to the first electrode184 and a second electrical wire 194 electrically coupled to the secondelectrode 186. During an ablation procedure, the ability to switch backand forth between the first and second electrodes 184, 186 allows theoperator to adjust between providing ablation over a relatively largearea via conduction through the balloon 174 or over a relatively small,focused area via the second electrode 186, which is in direct contactwith the tissue and which has a smaller contact surface area than theballoon 174.

In the embodiment of FIG. 9, a proximal section 196 a of the balloon 174is coupled to the distal section 172 of the elongate shaft 168. A distalsection 196 b of the balloon 174, in turn, is coupled to the distal end188 of the elongate shaft 168. In certain embodiments, the balloon 166has a composite structure formed from different polymeric materials. Inone embodiment, for example, the composite balloon 166 includes aproximal, non-conductive section 196 a made from a hydrophobic polymerand a distal, hydratable ionically conductive section 196 b made from ahydrophilic polymer. In some embodiments, for example, the compositeballoon structure can comprise a proximal section 196 a made from ahydrophobic polyurethane material and a distal section 196 b made from ahydrophilic polyurethane material such as TECOPHILIC 60D®. Otherpolymeric materials can be used to impart differing hydrophiliccharacteristics to the proximal and distal sections 196 a, 196 b.

When inflated with an electrically conductive fluid, the distal section196 b of the balloon 174 is rendered conductive by hydration due to theionic content of the fluid when the RF energy is supplied to the firstRF electrode 184. As a result, electrical current is transmitted throughthe fluid and into the tissue in contact with the distal section 196 bof the balloon 174.

The ablation device 166 can further include one or more featuresdescribed with respect to other embodiments, including one or moretemperature sensors for sensing the temperature of fluid within theballoon or on the surface of the balloon at the balloon-tissueinterface, and one or more electrocardiogram sensors for sensingelectrical activity in or near the heart. The device 166 can alsoinclude other features such as a spring-actuated plunger assembly. Incertain embodiments, the balloon 174 can also be made semi-permeable,allowing at least some of the pressurized fluid within the interiorsection 176 the balloon 174 to seep into the body at or near the targetablation site.

FIG. 10 is a flow diagram of an illustrative method 198 of performing anablation procedure of using an ablation device. FIG. 10 may represent,for example, several example steps that can be used in conjunction withthe ablation device 166 of FIG. 9 for performing ablation on cardiactissue. The method 198, however, can be performed using any of theablation devices described herein, and can be used for performing othertypes of ablation therapy. In one embodiment, for example, the method198 can be used for performing ablation therapy on brain tissue fortreating neurological disorders such as Parkinson's disease.

To perform the therapy, a clinician inserts the ablation device 166 intothe lumen of a guide catheter, and advances the ablation device 166 to aregion in or near the heart to be treated (block 200). In the treatmentof paroxysmal atrial fibrillation, for example, the clinician may insertthe guide catheter and ablation device into a main vein or artery (e.g.,a femoral artery), and advance the assembly through the vasculature intoposition within a heart chamber or cardiac vessel to be treated (e.g., apulmonary vein). In some embodiments, a steering mechanism within theguide catheter or within the ablation device 166 itself can be used tosteer the distal end of the device 166 into position to the desiredtreatment site.

Once in position, an electrically conductive fluid is then injected intothe balloon 174, causing the balloon 174 to inflate (block 202). Ifnecessary, the switch 190 on the RF generator 34 can then be set toactivate the first (i.e., balloon) electrode 184 (block 204), causingenergy to flow from the electrode 184 to the distal conductive section196 b of the balloon 174 through conduction through the fluid andballoon material. The clinician may then form a relatively wide lesionon the tissue by contacting the distal section 196 b of the balloon 174with the tissue (block 206).

The size and shape of the distal balloon section 196 b produces a lesionthat is very uniform in nature and is void of dehydrated or charredareas that can result in catheters that use an electrode in directcontact with the tissue to be ablated. In some procedures, the size andshape of the inflated balloon 174 can also facilitate formingoverlapping lesions to ensure a contiguous ablation line is created andthat the aberrant electrical conduction is completely blocked. In thoseembodiments in which the distal section 196 b is also porous, a steadyflow of electrically conductive fluid can be maintained throughout theablation period, which further serves to create an electrical pathwaybetween the balloon 174 and the body tissue.

If, during the ablation procedure, the operator desires to provide apin-point lesion on the tissue, the switch 190 can then be set tooperate using the second electrode 186 (block 208). Once set, the energyfrom the RF generator 34 is then transmitted to the second (i.e., tip)electrode 186, which directs RF energy directly into the tissue. Incontrast to the first electrode 184, which has a relatively largesurface area in contact with the tissue to be ablated, the secondelectrode 186 produces a smaller, focused ablation (block 210). Incertain procedures, for example, the second electrode 186 can be used togenerate narrow, focused ablation points whereas the first electrode 184can be used to generate wider, less-focused ablation points. The processof switching back and forth between each of the electrodes 184, 186 canbe repeated one or more times until the ablation procedure is complete.

Various modifications and additions can be made to the exemplaryembodiments discussed without departing from the scope of the presentinvention. For example, while the embodiments described above refer toparticular features, the scope of this invention also includesembodiments having different combinations of features and embodimentsthat do not include all of the described features. Accordingly, thescope of the present invention is intended to embrace all suchalternatives, modifications, and variations as fall within the scope ofthe claims, together with all equivalents thereof.

What is claimed is:
 1. An ablation device for treating body tissue,comprising: an elongate shaft having a proximal section, a distalsection, and at least one fluid lumen configured to receive anelectrically conductive fluid; an inflatable balloon coupled to thedistal section of the shaft and including an interior section in fluidcommunication with the at least one fluid lumen for actuating theballoon between a collapsed state and an expanded state, wherein theballoon comprises a composite structure having a proximal balloonsection including a first polymeric material and a distal balloonsection including a second polymeric material different from the firstmaterial, and the first polymeric material is a hydrophobic polymer andthe second polymeric material is a hydrophilic polymer; and at least oneelectrode located within the interior space of the balloon.
 2. Theablation device of claim 1, further comprising at least one additionalfluid lumen for recirculating fluid through the device.
 3. The ablationdevice of claim 1, wherein, in the expanded state, the balloon isconically shaped.
 4. The ablation device of claim 1, wherein the distalsection of the balloon is invaginated.
 5. The ablation device of claim1, wherein the distal section of the balloon is semi-permeable.
 6. Theablation device of claim 1, wherein a thickness of the balloon tapersalong a length of the balloon from the proximal balloon section to thedistal balloon section.
 7. The ablation device of claim 1, wherein theballoon comprises a multi-layered structure.
 8. The ablation device ofclaim 1, further comprising a temperature sensing element coupled to thedistal section of the balloon.
 9. The ablation device of claim 1,further comprising at least one electrocardiogram sensor coupled to thedistal section of the balloon.
 10. The ablation device of claim 1,further comprising a spring-actuated plunger assembly configured to biasthe balloon in the collapsed state.
 11. The ablation device of claim 10,wherein the plunger assembly comprises a plunger mechanism and a springconfigured to bias the plunger mechanism against the balloon.
 12. Theablation device of claim 11, wherein the plunger mechanism includes aplunger shaft and an atraumatic tip.
 13. The ablation device of claim12, wherein the plunger shaft is slidably disposed within the elongateshaft and the electrode.
 14. An ablation device for treating bodytissue, comprising: an elongate shaft having a proximal section, adistal section, and at least one fluid lumen configured to receive anelectrically conductive fluid; an inflatable balloon coupled to thedistal section of the shaft and including an interior section in fluidcommunication with the at least one fluid lumen for actuating theballoon between a collapsed state and an expanded state; at least oneelectrode located within the interior space of the balloon; and aspring-actuated plunger assembly configured to bias the balloon in thecollapsed state, the plunger assembly including a plunger mechanism anda spring configured to bias the plunger mechanism against the balloon,the plunger mechanism including a plunger shaft and an atraumatic tip,wherein the atraumatic tip is configured to disengage from the balloonin the expanded state.